1. Field of the Invention
The invention relates generally to devices for the treatment vascular disease and, more particularly, the invention relates to a filter device for placement within a blood vessel that is operable to catch and retain embolic material dislodged during the treatment of atherosclerotic disease.
2. Description of the Related Technology
Atherosclerotic disease in the coronary and carotid vasculature is one of the leading causes of morbidity and mortality in the United States. Atherosclerotic disease can cause insufficient circulation of oxygenated blood due to luminal narrowing caused by formation of atherosclerotic plaque. In addition, atherosclerotic disease can cause thromboembolism.
Atherosclerosis is a progressive, degenerative arterial disease that leads to occlusion of affected blood vessels, thereby reducing vessel patency, and hence, blood flow through them. During the course of this vascular disease, plaques develop on the inner lining of the arteries narrowing the lumen of the blood vessels. Sometimes these plaques become hardened by calcium deposits, resulting in a form of atherosclerosis called arteriosclerosis or xe2x80x9chardening of the arteries.xe2x80x9d Atherosclerosis attacks arteries throughout the body, but the most serious consequences involve damage to the vessels of the brain and heart. In the brain, atherosclerosis is the primary cause of strokes, whereas in the heart, when total blockage of an artery occurs, portions of heart muscle can die and disrupt the electrical impulses that make the heart beat.
The internal carotid artery is an artery often affected by atherosclerosis. When atherosclerosis is detected in the carotid artery, physicians need to remove the plaque, thereby restoring circulation to the brain and preventing a cerebral vascular accident.
Treatment for atherosclerosis ranges from preventive measures such as lowering fat intake and medication to endarterectomy, balloon angioplasty or atherectomy. In endarterectomy, the affected artery is surgically opened and plaque deposits are removed from the lining of the arterial wall. Occasionally during endarterectomy, large pieces of plaque break away from the arterial walls and enter the blood stream. Additionally, thrombotic material may develop if damage to the arterial wall occurs from the removal of plaque. Dislodged plaque deposits and thrombotic material, causing a condition called thromboembolism, may occlude smaller vessels downstream resulting in a vascular problems and potentially death. Thus, it is common practice by one skilled in the art to capture dislodged plaque, or any thrombotic material, by using a vacuuming procedure throughout the duration of the endarterectomy procedure. Although a significant percentage of plaque and thrombotic material is captured by this vacuuming procedure, pieces of plaque as well as thrombotic material inevitably escape.
Balloon angioplasty is a another method of treating atherosclerosis. In balloon angioplasty, a balloon-tipped catheter is inserted through the skin into the vessel and maneuvered to the lesion in the artery. The balloon tipped catheter is threaded through the lesion and inflated, increasing the vessel lumen to improve blood flow at the site. After deflating the balloon, stents are often inserted to keep the lumen of the vessel open, maintain blood flow and provide a scaffolding for tissue growth. Although balloon angioplasty and stenting are alternative methods of treatment, recent studies have documented adverse side effects associated with carotid stenting and, therefore, such procedures may not be as desirable as endarterectomy.
An additional method of treatment, atherectomy, is a procedure during which the plaque in coronary arteries is ground into minuscule particles that the body can clean from the bloodstream. Occasionally, during such procedures, large pieces of plaque break away from the arterial walls and enter the blood stream. As described above, this plaque debris can not be processed by the body and, therefore, must be vacuumed from the bloodstream to prevent the plaque from clogging arteries in the brain or elsewhere.
The primary use of blood filters historically has been to prevent pulmonary embolism. Blood filters are implanted within a vein, typically the inferior vena cava, and are intended to trap large blood clots while allowing blood to pass freely through the filter around the clot. In most cases trapped blood clots will normally dissolve over time.
Most often, blood filters are implanted within the inferior vena cava from a variety of peripheral vein access sites, for example, the jugular or femoral veins. An early example of such a filter was the Mobin-Uddin (MU) umbrella filter, which was developed and made available by American Edwards Laboratories in Santa Monica, Calif. in the 1970s. The Mobin-Uddin umbrella was composed of six flat ELGILOY spokes radiating from a hub and partially covered by a web designed to capture blood clots. MU filters were introduced into the body via a cutdown of the jugular or femoral vein and subsequent passing of a catheter through the access site to the filter implant site in the infrarenal inferior vena cava. While this method was an improvement over previous methods, the MU filter was associated with a high incidence of occlusion of the inferior vena cava, in which blood flow through the vena cava was completely obstructed.
In the mid-1970""s, the Kimray-Greenfield (KG) vena cava filter was introduced. The original KG filter is conical in shape and is composed of six stainless steel wires equally spaced with its apex cephalad. Although the filter was originally placed using a local cutdown of the jugular or femoral vein, it was later adapted to be inserted percutaneously. The KG filter is designed to capture clots 7 mm or greater in diameter, holding the clots in the infrarenal vena cava until the body""s own lytic system dissolves the clot. The principal drawbacks of the KG filter are the possibility of tilting and filter migration, often related to a failure to open, or untimely ejection of the filter from the introducer.
Subsequent versions of the so-called Greenfield filter were developed to reduce the size of the introducer catheter to facilitate percutaneous introduction. Other vena cava filters were introduced in the United States in the late 1980s, including the Vena Techxe2x80x94LGM vena cava filter, the Bird""s Nest vena cava filter, and the Simon-Nitinol vena cava filter. The Vena Techxe2x80x94LGM filter is a conical filter made from the PHYNOX alloy, with longitudinal stabilizing legs in addition to the intraluminal cone. The Bird""s Nest filter is a xe2x80x9cnestxe2x80x9d of stainless steel wire which is wound into the vena cava, while the Simon Nitinol filter is a two-stage filter made from nickel-titanium alloy with a conical lower section and a petal-shaped upper section. All of these devices are permanent implants which cannot be removed from the body without a major surgical intervention.
Among numerous vena cava filters introduced in Europe but never brought to the United States was the optimal central trapping (OPCETRA) filter. The OPCETRA filter has two main parts: a main basket with ten, long stainless steel wire arms and a distal basket with five, short stainless steel wire arms. This design gives the filter an hourglass shape which provides a self-orienting structure for the filter within the lumen of a blood vessel. The OPCETRA filter was also a permanently implanted vena cava filter.
All of the above-identified vena cava filters are inserted into the body by passing the filter through a catheter to the site of deployment in the infrarenal inferior vena cava. After ejection from the catheter, these filters open or are manually deployed until the filter anchoring elements engage the vessel wall. These filters often have hooks or some other means by which the filter becomes fixed permanently to the vessel wall.
For an important subset of patients, in particular young trauma patients and patients undergoing total hip or knee replacement surgery, the risk of embolism is short-term and limited to a definable period of time. Because of the long-term risks associated with implantation of a permanent blood filter, including venous stasis due to caval occlusion and its related complications, patients whose risk period is limited are not considered good candidates for permanent blood filters. The search for an appropriate temporary therapy for such patients lead to the development of temporary, tethered removable filters.
Tethered temporary filters are attached to a catheter and are implanted in the infrarenal vena cava with the tethering catheter extending out of the puncture site in the neck or groin, or buried subcutaneously within the soft tissues in the patient""s neck. The tether remains coupled to the filter after deployment. The tether is then used to retrieve the filter. The potential for septic complications associated with the tethering catheter exiting the -neck or groin require removal of such devices within fourteen days of placement. Risk periods for embolism in such patients, however, can extend up to twenty-one weeks.
Temporary retrievable filters which are not attached to a tethering catheter have a construction similar to some versions of permanent filters. A hook or similar grasping structure is provided to allow a snare to engage the filter during the retrieval procedure. The filter in its entirety is then retrieved using a snare by drawing it into a catheter. However, to ensure the filter does not migrate within the vessel, barbs, anchors or similar structures must be used to engage the filter with the interior wall of the vessel for retaining it in place. These anchors make removal without injuring the vessel difficult. Moreover, after a relatively short period of time the portion of the filter legs in contact with the vessel wall are incorporated by endothelial tissue making retrieval difficult or impossible.
More recently, it has been proposed to provide a removable filter in two parts. An anchoring part of the filter engages the vessel walls, and become incorporated by endothelial tissue. A filter part is releasably coupled to the anchoring part. After the risk of embolism has passed, the filter part may be retrieved using a snare and catheter.
Thus, there is a need for a temporary, convertible blood filter that can be inserted into a vessel to treat vascular disease. Additionally, there is a need for a temporary, convertible blood filter to catch and retain biological debris during procedures such as endarterectomy, angioplasty, or atherectomy, yet be openable to fully restore vessel patency following the treatment.
The invention provides a filter arranged to be disposed within a blood vessel. The filter includes intraluminal filter elements and is convertible from a filter configuration to an open, stent-like configuration.
The invention also provides a method of treating embolism and atherosclerotic disease using a filter constructed in accordance with the invention.
In a preferred embodiment, the filter device includes a plurality of elements formed into a single cone or dual cone filter structure. A retainer secures the elements in an intraluminal filter configuration upon initial deployment within a vessel. The retainer is then either self-releasing or removable to permit the legs to expand from the filter configuration into what may generally be described as an open or stent-like configuration substantially, totally reopening the lumen.
To maintain stability within the lumen, superior and/or inferior ends of the filter can be formed with a small barb or hook that engages the interior wall of the vessel.
A single cone filter in accordance with the invention includes a plurality of intraluminal filter elements, the superior ends of which are joined by a releasable retainer. In one preferred embodiment, a filter web extends between the plurality of intraluminal elements. In another preferred embodiment, the single cone filter has filter legs which are constrained in the filter configuration. In yet another preferred embodiment, a spring member couples to the legs of the single cone filter to urge them radially outward and revert the filter to an open or stent-like configuration. When in the open configuration, the lumen is substantially unobstructed by the filter.
A dual cone filter in accordance with a preferred embodiment of the invention has intraluminal filter elements joined by a releasable retainer at a location between their superior and inferior ends. In one embodiment, a filter web extends between the intraluminal filter elements. This dual cone shape advantageously improves the self-orienting mechanism of the filter. A spring may join the legs to urge them from the dual cone or hourglass shape into a stent-like configuration upon release of the retainer. Alternatively, the legs may be formed to provide the restoring force.
In still another embodiment, the filter device has intraluminal elements made of a biodegradable material.
In yet another embodiment, the filter device has a releasable retainer joining both ends of the of the intraluminal elements to create a basket-like configuration. The retainer may be self-releasing or removable to permit the intraluminal filter elements to expand from a basket-like configuration into a single cone configuration and subsequently into what may generally be described as an open or stent-like configuration.